It may very well be that some of the things we regard as psychiatric illnesses will be found to be neurological illnesses. But it is also the case that some things we regarded as psychiatric illnesses come to be seen as social prejudices against patterns of conduct no longer disapproved of. And to confound matters, unless some conduct has magical, Cartesian causes, presumably socially disapproved of conduct correlates with neurological stuff of some kind, which differs from the neurological stuff that correlates with approved conduct. But that wouldn’t make it a disease. Maybe it is and maybe it isn’t.
So there’s a big, messy problem here, and it is due to the fact that psychiatry is unusual in that most of its “symptoms” are conduct (and yes, from the third person point of view, thoughts and feelings manifest themselves as conduct too), and while it is in some sense straightforward to say that oily black vomit doesn’t look like the sort of thing that is supposed to come out of mouths, what about socially unacceptable speech? Where is the model for “healthy, normal” speech going to come from?
Now I am certainly not denying that there are neurological diseases, nor am I denying that some psychiatric illness models/descriptions/symptom-criteria will be replaced by more straightforwardly neurological ones (so I fully appreciate the limits of a kind of global Szaszian skepticism). But as long as you have a branch of medicine which regards socially meaningful conduct as medical symptom, you’re going to be entangled with more than merely biological normativity, and your classifications, diagnostic criteria, etc. will be inevitably, as we pomo philosophers say, a site of contestation. Rather than figure out who is right, the Szaszian skeptics, the neurological reductionists or the traditional psychiatrists, I think we should just realize that this is an interminable discussion in which there can’t really be any winners except in specific cases, and there, perhaps only temporarily. The conduct described as “complaining about the death of your child” nine months after her death used to be considered socially appropriate, and done in a certain fashion, perhaps even obligatory. Now it is a disease. The state of our knowledge has not changed: we have.